“Janmarcos was a kid full of love, full of happiness, and always had a lot of energy,” she said. Whenever a friend was sad, she added, Janmarcos would always try to comfort them, saying, “Aww, it’s OK.”

Janmarcos was shot to death last Friday in his Mattapan home, allegedly by his older brother, who now faces juvenile charges, including involuntary manslaughter.

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“He was really, really sweet,” she said before heading into the funeral home. “He was funny, and he used to tell a lot of jokes.”

Inside the wake, mourners packed the room, sitting in chairs or crowding around the casket, weeping audibly. One woman sighed, saying quietly, “Ay, amor” as she wiped tears from her face.

A bunch of mylar balloons in the shape of hearts and stars hung over the child’s open casket.

“Our thoughts and prayers are with you during this difficult time,” read a note in an arrangement of red roses and white flowers topped by a picture of the curly-haired boy.

Laminated cards, with Janmarcos’s photo and a prayer written in Spanish were handed out. “Help me from the dangers of the world. . . . I want the way I live my life to make you smile,” the prayer read in part.

Jessica Rinaldi For The Boston Globe

A wake was held Wednesday at a Jamaica Plain funeral home for Janmarcos Pena, 9, who allegedly was slain by a sibling.

Mourners wore buttons emblazoned with the boy’s smiling face.

Shortly after 9 p.m., mourners released some of the balloons into the night sky.

‘Their hearts ache, and so does the heart of the city of Boston.’

Young children could be heard talking as the balloons rose, and one youth remarked, “That’s Janmarcos watching us.”

Police and prosecutors say that Janmarcos’s 14-year-old brother, who has not been identified, was playing with a gun in their Morton Street home when he shot his younger sibling, apparently by accident.

The older boy is being held on $50,000 cash bail in the custody of the state Department of Youth Services. He has denied the charges.

The Globe has reported the state Department of Children and Families had attempted to take custody of the older brother, who has a history of violent episodes, but a judge denied the agency’s request.

In a statement released Wednesday by the Boston public schools, the principal of the Hennigan School said students and faculty were “devastated by the tragic event Friday.”

“We’ve had counselors here at the school since Friday, and they’ve done an extraordinary job of supporting us during this truly sad time,” the statement read. “Our condolences go out to the boy’s family.”

Speaking softly to a reporter outside the funeral home, Jackson said he did not know the family personally but wanted to extend his condolences.

“Their hearts ache, and so does the heart of the city of Boston,” Jackson said. “I think any loss of a child is a loss of our future, and I’m here to be supportive of the family.”

About two hours after the wake began, mourners began to trickle out, many with eyes puffy and red-rimmed. Most declined to talk.

“I’m sorry,” one man said as he escorted a woman who was beginning to cry again, “it’s bringing back memories.”

As she left, Maria Cordon, principal of the Hennigan School, recalled Janmarcos, holding back tears as she spoke.

“He was just a beautiful child, just everything: his innocence, just the way he got along with all the kids, his sensitivity, his smarts,” she said. “I had too many kids in there today, too many parents. . . .

“He was too little, too young.”

A funeral Mass for Janmarcos is scheduled Thursday morning at Our Lady of Lourdes Church in Jamaica Plain.

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